Antea Group’s client owned a 180-acre manufacturing facility where materials had been disposed of from 1900 to the present. The company, under regulatory oversight by both USEPA and MassDEP, was required to define the sources, nature and extent of releases from these disposal practices.
To complicate the project, many of the disposal areas on the 180-acre facility were located on active process areas or structures. The subsurface geology was known to consist of a complex glacial depositional environment, with a confining unit as deep as 100 feet, where volatile organic compounds (VOCs) had been detected, including chlorobenzene and chlorinated VOCs (CVOCs).
Antea Group’s challenging scope of work included:
- Defining the source, nature and extent of disposal areas, including 4 landfills encompassing 26 acres
- Assessing 72 additional USEPA-defined Solid Waste Management Units (SWMUs) and Areas of Concern (AOCs)
- Characterizing risks to human health and environment using a combination of the significantly different MassDEP and USEPA risk assessments
- Evaluating and selecting appropriate remedial options where applicable
To assess the source, nature and extent of disposal areas, Antea Group collaborated with the client and the regulatory agencies in developing data objectives and work plans agreeable to all. Antea Group’s human health and environmental risk assessment was based on extensive activities that included:
- Geophysical studies magnetometer and Global Positioning System (GPS) surveys
- Examination of 10,000 feet of soil from over 300 soil borings
- Collection and analysis of 250 soil or waste samples
- Installation of 130 monitoring wells
- Collection and analysis of over 750 groundwater samples
- Site-specific compound analysis
- Collection and analysis of almost 50 sediment and surface water samples
- Collection and analysis of 80 vapor samples from pore water of river beds (passive vapor diffusion)
- Studies of 3D models of groundwater flow, geology and contaminate extent
The risk assessments were so conducted that they satisfied both the USEPA and MassDEP requirements.
Antea Group achieved an impressive result encompassing the following achievements:
- A No Further Action letter for 82 of the 87 SWMU and AOC disposal areas, assuming application of institutional controls for industrial land use
- A low priority environmental status with the agencies using established screening tools. These tools also allowed for oversight through a Massachusetts Licensed Site Professional (LSP) instead of MassDEP
- Satisfaction for the client that the site had been adequately delineated
- Acceptance of the risk assessment outcome by both USEPA and MassDEP
Monitored natural attenuation was demonstrated on the CVOCs, although residual recalcitrant CVOC residual persisted. These CVOCs were allowed to exist onsite upon demonstration that complete biodegradation of the CVOCs occurred prior to reaching the river groundwater surface water interface in the hyporheic zone, where the subsurface is naturally rich in oxygen, microbial communities and nutrients. Given Antea Group’s site knowledge and trusting relationship with the agencies, the study feasibility and remedial implementation portions of the project were sole sourced.